A fallen arch or flatfoot is a deformity that affects people young and old. It is a skeletal misalignment deformity in which the arches of the foot collapse resulting in the entire sole of the foot being in complete or nearly complete contact with the ground. As there is a biomechanical relationship between the foot and lower leg, problematic issues in the inner workings of the foot structure adversely affect the rest of the body.
In proper operation the structure of a healthy arch provides an elastic connection between the hind foot and forefoot which serves to safeguard the body during weight bearing activities by displacing the impact force before it reaches the leg bones. For persons afflicted with one or both feet suffering from a flat foot condition, this elastic absorption of the foot is diminished, if not entirely non-existent. Moreover, in addition to being painful, pathologic flatfeet may cause bunions, hammertoes, heel spurs, arch pain, growing pains, shin splints, knee pain, and back pain.
Of the many bones within the human foot, the flatfoot condition is clearly evidenced by the head of the talus bone being displaced medially and distally from the navicular bone, which in turn causes lateral misalignment throughout the foot as the talus and navicular tend to move outward. In addition, there is a change in relative alignment in the subtalar joint that occurs at the meeting point between the talus bone and the calcaneus bone such that the canal which should naturally occur between them is depressed. This canal is commonly referred to as the sinus tarsi.
The subtalar joint has a neutral position where there are neutral forces passing through the multiple axis and planes that make up and permit the natural triplanar motion of the joint. When the subtalar joint's relaxed position is no longer in the intended neutral position, then the translation of forces placed on the surrounding joints, ligaments and osseous structures is abnormal. Simply put, the misalignment of the talus and calcaneus bones further imposes misalignment on other foot bones.
It has been discovered that by re-establishing the relative alignment between the talus and calcaneus bones, the overall arch structure of the foot can be reestablished as well. While this can be demonstrated by physically manipulating a person's foot, such physical manipulation is impractical during a normal use of the foot. As such there have been various efforts made to provide implants which operate to physically reposition and realign the talus and calcaneus bones.
Various implants have been developed of varying shapes and materials, such as Titanium, stainless steel, silicone, polyethylene and PEEK. The goal of such implants is to stabilize the talus and calcaneus bones with respect to each other without fusing them. While perhaps effective at reestablishing an improved alignment of the talus and calcaneus bones the options for implants known to date fall short of truly reestablishing the triplanar motion and naturally gliding motion of the subtalar joint.
One such effort is set forth in the prior art reference of Maxwell U.S. Pat. No. 6,168,631 teaching a Subtalar Implant System and Method for Insertion and Removal. Maxwell specifically teaches an implant sized and shaped to fit within the sinus tarsi, and that the implant has exterior threads so as to engage the tissues, i.e. bones, of the sinus tarsi. Maxwell also teaches that the implant is preferably made from a titanium based alloy as Maxwell asserts that it is an object of the invention not to deform under post operative compressive forces. While perhaps effective in re-establishing spacing between the talus and calcaneus bones, as the Maxwell implant is quite literally screwed in-between them, the screwing nature also binds them and substantially eliminates the natural triplanar motion of the subtalar joint. In addition, the metal nature of the Maxwell implant results in the patient experiencing a hard stop—the foot simply does not move in some directions and the resistance to compression can be painful. In addition, over time and as a result of repeated use of the repaired foot, the Maxwell implant may actually abrade, or cause the surrounding bone tissues to abrade—leading to shards of foreign or natural material within the subtalar joint further causing pain and perhaps requiring surgical extraction of the debris, and/or the Maxwell implant itself as suggested by the title.
The prior art reference of Lepow U.S. Pat. No. 8,092,547 for a Subtalar Implant Assembly teaches an implant with a core region 16 that is tapered between a first end 24 and a second end, the core region 16 further having a threaded region 18 formed on and extending outward. As with the Maxwell implant, the Lepow implant is screwed into place between the talus 38 and calcaneus 40 bones. As such, once again, this screwed in nature binds the talus and calcaneus bones and substantially eliminates the natural triplanar motion of the subtalar joint. Lepow also teaches forming the core region from various plastics, metals, metal alloys, glass, ceramics, composite materials such as carbon fiber, bio-absorbable materials, or the like and combinations of metals and/or plastics. Once again the Lepow implant is intended to be a very solid non-deformable implant. As such, the motion of the foot may be un-natural and perhaps painful for some person's, and once again shards of natural and foreign materials may develop within the subtalar joint resulting in pain and the need for surgical extraction.
The prior art reference of Graham U.S. Pat. No. 7,033,398 for a Sinus Tarsi Implant is yet another threaded implant. The Graham implant is specifically taught to have a first member 106 with an outer surface generally configured in the shape of a right conical frustrum between a second member 108 and a cylindrical third member 110, the third member 110 being sized to fit within the sinus tarsi. Preferably fashioned about the cylindrical third member 110 is a tissue engagement surface more specifically taught as one or more channels 112, which in a preferred embodiment are a continuous thread. Once again, the Graham implant is intended to be screwed into place with the one or more channels 112 of the third member 110 binding with the talus and calcaneus bones proximate to the sinus tarsi. And again, such binding likely eliminates the natural triplanar motion of the subtalar joint. The Graham implant is also taught to be constructed of by a polymer which is substantially incompressible and tough, once again potentially resulting in an uncomfortable if not painful implant for some person's. And again, the binding nature of the Graham implant may once again result in shards of foreign or natural material within the subtalar joint.
Other threaded implant prior art references exist as well, such as Pech U.S. Pat. No. 9,125,701 and Katz U.S. Pat. No. 7,679,153. As noted in the details above, it is a clear aspect of a threaded implant to be screwed in-between the talus and calcaneus bones, so as to bind them in a restored alignment, but in tradeoff for this bound alignment the natural triplanar motion of the subtalar joint is substantially reduced if not completely eliminated. The stress and force imparted by this unnatural elimination may and often does cause abrasion of implant and or bone tissue.
The prior art reference of Rappaport U.S. Pat. No. 4,450,591 teaches an Internal Anti-Prorotary Plug Assembly and Process of Installing the Same. Rappaort departs from the threaded implant approach. As taught by Rappaport, a biocompatible plastic cone shaped plug is provided with a tie line extending from the minor base of the plug. After being inserted into the sinus tarsus or opening of the subtalar joint, the tie line is bound about the deltoid ligament to hold the cone shaped plug in place. While perhaps avoiding the bound alignment imposed by a threaded implant, the tie line may cause insult and abrasion to the tendon as compressive forces upon the conical shaped body result in the generation of lateral forces upon the plug and thereby tension the tie line. Further, the plastic may still abrade or cause the talus and calcaneus bones to abrade.
Moreover, although there are a growing number of implants and procedures which strive to alleviate some of the issues associated with flatfoot by stabilizing the subtalar joint, in the main they appear to sacrifice the natural and expected gliding motion of the joint for improved relative spacing. In addition, as this reduced natural and expected gliding motion is known to often cause abrasion, extraction and replacement of the implants appears to be an expected likelihood in the future, subjecting the patient to an additional surgical procedure as well as potential pain and discomfort when and if the implant breaks down or abrades body tissues.
Hence there is a need for a system and method that is capable of overcoming one or more of the above identified challenges.